A color pattern on an animal where the upper side is darker and the lower side is lighter, helping it blend into its environment.
From counter- + shade (from Old English scead, shadow). The term was coined in early 20th-century biology to describe a specific camouflage adaptation.
Many fish and sharks use countershading—dark on top so they blend with the ocean floor when viewed from above, light underneath to match the sky when viewed from below. It's nature's perfect disguise.
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